Owing to a technological development for mass production, an easy driving means, a low power consumption, a high picture quality and a realization of large screen, a liquid crystal display (LCD) device is appropriate for a portable device, and furthermore its application field has gradually increased.
According to a method for controlling an alignment of a liquid crystal layer in the LCD device, the LCD device may be developed in various modes, for example, Twisted Nematic (TN) mode, Vertical Alignment (VA) mode, In-Plane Switching (IPS) mode, Fringe Filed Switching (FFS) mode, etc.
In case of the IPS mode, both a pixel electrode and a common electrode are alternately arranged in horizontal direction, whereby a horizontal electric field is generated between the pixel electrode and the common electrode to control an alignment of a liquid crystal layer. In case of the FFS mode, a pixel electrode and a common electrode are provided at a predetermined interval from each other and an insulating layer is interposed between the pixel electrode and the common electrode, whereby a fringe field is generated between the pixel electrode and the common electrode to control an alignment of a liquid crystal layer.
The liquid crystal display device of the IPS mode is processed with a gamma tuning for improving a residual image. The common voltage and a center voltage before gamma tuning will be described with reference to FIG. 1a. 
FIG. 1a is a view illustrating a common voltage (Vcom) and a center voltage (Vcenter) before gamma tuning.
Referring to FIG. 1a, a related art liquid crystal display device before gamma tuning uses a common voltage and a gamma voltage. A gamma data of the related art liquid crystal display device includes a positive gamma curve and a negative gamma curve which are symmetrical to each other with respect to the common voltage. The gamma voltage is generated by using the gamma data. The common voltage has the same voltage level as that of the center voltage of the positive gamma curve and the negative gamma curve. Therefore, the center of the gamma voltage is identical to the center voltage (Vcenter). The term “center voltage” may be referred to as the center voltage of the positive gamma curve and the negative gamma curve for each gray level (e.g., G0 to G255 in case of 8 bits and 255-gray).
In other words, the positive gamma curve and the negative gamma curve may be symmetrical for each gray level with respect to the center voltage (Vcenter) which is identical to the common voltage. Therefore, the common voltage of the related art liquid crystal display device is identical to the center voltage (Vcenter), and has a certain voltage level according to the gray level.
In addition, the positive gamma curve and the negative gamma curve are alternatively applied to a pixel array for polarity inversion of the pixel array for each frame to prevent damage on the liquid crystal layer of the related art liquid crystal panel. In theory, when the positive gamma curve and the negative gamma curve are symmetrical to each other with respect to the common voltage, flicker and the residual image may be minimized. For example, in gray level G0, the positive gamma curve is 4.5V and the negative gamma curve is 3.5V. Therefore, with respect to the common voltage, the positive gamma curve has 0.5V potential difference. And, with respect to the common voltage, the negative gamma curve has 0.5V potential difference. Therefore, the potential differences of the positive gamma curve and the negative gamma curve are the same.
However, in the real driving environment, there is a problem of flicker and residual image phenomenon because of the various reasons such as electrical resistance, parasitic capacitance and thermal stress of the liquid crystal panel when the common voltage is identical to the center voltage.
Before gamma tuning, due to the above various reasons, the desired optimal common voltage (Optimal Vcom) for each gray level of the related art liquid crystal display device is analyzed as non-uniform. That is, each gray level requires different optimal voltages to minimize the flicker and residual image problem. However, the related art liquid display device can use only one common voltage as the common electrode is commonly connected with the pixel array. Therefore, even though the non-uniform optimal common voltages (Optimal Vcom) for each gray level are evaluated, the non-uniform optimal common voltages cannot be applied to the related art liquid crystal display device. Thus, the image quality is deteriorated.